I had some mp3 audio tracks playing back slowed down. I updated the mixer frequency to be based on the mp3 sample rate using mutagen like so:
import pygame, mutagen.mp3
song_file = "your_music.mp3"
mp3 = mutagen.mp3.MP3(song_file)
pygame.mixer.init(frequency=mp3.info.sample_rate)
pygame.mixer.music.load(song_file)
pygame.mixer.music.play()
And it fixed the problem.